The field of this invention relates to shock isolators and more particularly to a spring damper which employs the use of a compressible solid material, such devices to have different damping rates depending upon the direction of stroke.
The shock isolator of this invention has been found to be especially useful in automobiles to be located between the body of the vehicle and the bumper. However, it is considered to be within the scope of this invention to employ the apparatus of this invention in any other environment as it is well known that spring damping apparatuses are used in numerous fields.
Automobiles have always employed some means to protect the body of the vehicle from slight bumps. Such means have normally been bumpers which are located in the front and rear portions of the vehicle. The bumpers are normally formed of a rigid piece of material, such as steel, which is rigidly secured to the vehicle. Upon the vehicle being struck by another vehicle, or the vehicle striking a fixed object, the material of construction of the bumper normally fails upon incurring even a quite small impact force. Additionally, such bumpers normally directly transmit the force into the vehicle itself. Such transmission of force is undesirable since it causes further damage to the vehicle.
Other bumpers have been developed for vehicles which absorb impact forces and do not normally transmit any significant amount of force to the vehicle structure itself as a result of normal impact forces.
In some cases, these bumpers incorporate energy absorbing units which make use of compressible solid material as the working medium. The compressible solid material has the capability of absorbing the impact load during extension of the piston into the material, and after extension thereof automatically causes the piston to be retracted back to its initial position. These devices using compressible solids have usually employed a fixed orifice area on the piston head which was primarily designed for the absorbing of the energy during the extension movement with little consideration being given to the retraction movement. Therefore, the retraction would be accomplished in an extremely low rate because the orifice area is required to be quite small for energy absorption. Further, in low temperature applications, the compressible solid material tends to increase in shear strength which may prevent prompt retraction of the piston.